Automobile's bodies, household electrical appliances or the like are commercialized by forming metal moldings from metal materials such as a steel sheet, a galvanized steel sheet, an aluminum alloy or the like, coating and assembling. Coating of such metal moldings are conducted after performing various steps such as degreasing, surface conditioning, chemical conversion treatment, and electrodeposition.
Surface conditioning is a treatment applied in such a way that a coat consisting of phosphate crystals is formed uniformly and quickly with a high density on the whole surface of metal in chemical conversion treatment of a phosphate coat of the subsequent step, and a treatment in which crystal nuclei of phosphate are generally formed on the metal surface by immersing a metal in a surface conditioning tank.
For example in Japanese Kokai Publication Sho-59-226181, there is disclosed a method of pretreating a metal surface, characterized by pretreating a metal surface by a prewash bath including titanium phosphate dispersed finely or tertiary zinc phosphate and montmorillonite, dispersed finely, prior to phosphating by a zinc phosphate solution. Technology disclosed therein is a method of sustaining an effect of a prewash bath for a long time.
However, a sustained effect of a prewash bath disclosed therein represents the stability of dispersion in a treatment bath of a dilute surface conditioner which is employed in a surface conditioning (pretreatment) and it cannot be said that the stability of dispersion in the concentrated solution (liquid concentrate) for preparing a surface conditioner is sufficient. With respect to a surface conditioner, it is generally stored in the form of a concentrated solution for preparing a surface conditioner and adjusted to a surface conditioner of a predetermined concentration by diluting the concentrated solution for preparing a surface conditioner in using it (in conducting the surface conditioning actually).
When the stability of dispersion of the concentrated solution for preparing a surface conditioner is not high, some ingredients such as zinc phosphate particles in the concentrated solution may precipitate and flocculate during storage. When the ingredients in the concentrated solution have precipitated and flocculated, the concentrated solution needs to be first stirred to homogeneously disperse the ingredients in the solution in adjusting a surface conditioner by diluting the concentrated solution. And, there maybe cases where the ingredients cannot be homogeneously dispersed even by stirring depending on the extent of precipitation and flocculation.
That is, when the stability of dispersion of the concentrated solution for preparing a surface conditioner is not high, a problem that a work of stirring and dispersing the concentrated solution becomes necessary or it becomes impossible to attain a desired effect of a surface conditioning because the ingredients cannot be homogeneously dispersed even by stirring may arise. Therefore, it is desired to develop a substance which is superior not only in the stability of dispersion of the surface conditioner but also in the stability of dispersion of the concentrated solution for preparing a surface conditioner.
And, in Japanese Kokai Publication Hei-10-245685, there is disclosed a pretreatment solution for conditioning a surface before applying chemical conversion treatment of a metal phosphate coat, which contains one or more species selected from phosphate containing at least one species of bivalent or trivalent metals including particles having a particle diameter of 5 μm or less, alkali metal salt or ammonium salt or a mixture thereof, and at least one species selected from the group of oxide fine particles bearing anionic charges and dispersed, an anionic water-soluble organic polymer, a nonionic water-soluble organic polymer, an anionic surfactant and a nonionic surfactant, and is adjusted to pH 4 to 13.
Further, in Japanese Kokai Publication 2000-96256, there is disclosed a treatment solution for conditioning a surface before applying chemical conversion treatment of a phosphate coat, which contains particles of one or more species of phosphate selected from phosphate containing one or more species of bivalent and/or trivalent metals and further contains (1) one or more species selected from monosaccharides, polysaccharides and derivatives thereof, or (2) one or more species of orthophosphoric acid, polyphosphoric acid or organic phosphonic acid compounds, or (3) one or more species of water-soluble high polymer compounds which consists of polymer of vinyl acetate, its derivative or copolymer of monomer being copolymerizable with vinyl acetate and vinyl acetate, or (4) polymer or copolymer obtained by polymerizing at least one species selected from specific monomers or α, β unsaturated carboxylic acid monomers, and monomer being copolymerizable with the above monomer in an amount of 50% by weight or less.
However, a treatment solution for surface conditioning disclosed therein is low in the stability of dispersion in a treatment solution, particularly in the stability of dispersion in a concentrated treatment solution. And, even when an inorganic dispersant is used, the stability of dispersion of the concentrated solution for preparing a surface conditioner is particularly insufficient in using a silica dispersant.